This invention relates generally to overcoatings for ionographic or electrophotographic imaging and printing apparatuses and machines, and more particularly is directed to an effective overcoating for a donor means like a roll, preferably with electrodes closely spaced therein to form a toner cloud in the development zone to develop a latent image. The present invention is directed in embodiments to suitable charge relaxable overcoatings especially for the transport means in systems like scavengeless or hybrid scavengeless development systems, reference for example U.S. Pat. Nos. 4,868,600, 5,172,170, and copending patent applications U.S. Ser. No. 396,153 (now abandoned) and U.S. Ser. No. 724,242 now abandoned, the disclosures of which are totally incorporated herein by reference.
Overcoatings for donor rolls are known and can contain a dispersion of conductive particles, like carbon black, or graphite in a dielectric binder, such as a phenolic resin or fluoropolymer, as disclosed in U.S. Pat. No. 4,505,573. The dielectric constant of the overcoatings ranges from about 3 to about 5, and preferably is about 3, and the desired resistivity is achieved by controlling the loading of the conductive material. However, very small changes in the loading of conductive materials near the percolation threshold can cause dramatic changes in resistivity. Furthermore, changes in the particle size and shape of such materials can cause wide variations in the resistivity at constant weight loading. A desired volume electrical resistivity of the overcoating layer is in the range of from about 107 ohm-cm to about 1013 ohm-cm, and preferably, the electrical resistivity is in the range of 108 ohm-cm to about 1011 ohm-cm. If the resistivity is too low, electrical breakdown of the coating can occur when a voltage is applied to an electrode or material in contact with the overcoating. Also, resistive heating can cause the formation of holes in the coating. When the resistivity is too high, for example about xcx9c1013 ohm-cm, charge accumulation on the surface of the overcoating creates a voltage which changes the electrostatic forces acting on the toner. The problem of the sensitivity of the resistivity to the loading of conductive materials in an insulative dielectric binder is avoided, or minimized with the coatings of the present invention.
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image of an original document being reproduced. This records an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed. Two component and single component developer materials are commonly used for development. A typical two component developer comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. A single component developer material typically comprises toner particles. Toner particles are attracted to the latent image forming a toner powder image on the photoconductive surface, the toner powder image is subsequently transferred to a copy sheet, and finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
The concept of trilevel, highlight color xerography is described in U.S. Pat. No. 4,078,929 (Gundlach). This patent discloses trilevel xerography as a means to achieve single-pass highlight color imaging wherein a charge pattern is developed with toner particles of a first and second colors. The toner particles of one of the colors are positively charged and the toner particles of the second color are negatively charged. In one embodiment, the toner particles are presented to the charge pattern by a pair of magnetic brush development systems wherein each system supplies a toner of one color and one charge.
In highlight color xerography (Gundlach), the xerographic contrast on the charge retentive surface or photoreceptor is divided into three levels, rather than two levels as is the situation for conventional xerography. The photoreceptor is charged, typically to xe2x88x92900 volts, and is exposed imagewise, such that one image corresponding to charged image areas (which are subsequently developed by charged-area development, CAD) remains at the full photoreceptor potential (Vcad or Vddp). The other image is exposed to discharge the photoreceptor to its residual potential, for example Vdad or Vc (typically xe2x88x92100 volts) which corresponds to discharged area images that are subsequently developed by discharged area development (DAD) and the background areas exposed such as to reduce the photoreceptor potential to halfway between the Vcad and Vdad potentials, (typically xe2x88x92500 volts) and is referred to as Vwhite or Vw. The CAD developer is typically biased about 100 volts closer to Vcad than Vwhite (about xe2x88x92600 volts), and the DAD developer system is biased about 100 volts closer to Vdad than Vwhite (about xe2x88x92400 volts).
The viability of printing system concepts such as trilevel and highlight color xerography usually requires development systems that do not scavenge or interact with a previously toned image. Since several known development systems, such as conventional magnetic brush development and jumping single component development, interact with the image receiver, a previously toned image will be scavenged by subsequent development, and as these development systems are highly interactive with the image bearing member, there is a need for scavengeless or noninteractive development systems.
Single component development systems use a donor roll for transporting charged toner to the development nip defined by the donor roll and photoconductive member. The toner is developed on the latent image recorded on the photoconductive member by a combination of mechanical and/or electrical forces. Scavengeless development and jumping development are two types of single component development systems that can be selected. In one version of a scavengeless development system, a plurality of electrode wires are closely spaced from the toned donor roll in the development zone. An AC voltage is applied to the wires to generate a toner cloud in the development zone. The electrostatic fields associated with the latent image attract toner from the toner cloud to develop the latent image. In another version of scavengeless development, isolated electrodes are provided within the surface of a donor roll. The application of an AC bias to the electrodes in the development zone causes the generation of a toner cloud. In jumping development, an AC voltage is applied to the donor roll for detaching toner from the donor roll and projecting the toner toward the photoconductive member so that the electrostatic fields associated with the latent image attract the toner to develop the latent image. Single component development systems appear to offer advantages in low cost and design simplicity. However, the achievement of high reliability and simple, economic manufacturability of the system continue to present problems. Two component development systems have been used extensively in many different types of printing machines.
A two component development system usually employs a magnetic brush developer roller for transporting carrier having toner adhering triboelectrically thereto. The electrostatic fields associated with the latent image attract the toner from the carrier so as to develop the latent image. In high speed commercial printing machines, a two component development system may have lower operating costs than a single component development system. Clearly, two component development systems and single component development systems each have their own advantages. Accordingly, it is considered desirable to combine these systems to form a hybrid development system having the desirable features of each system. For example, at the 2nd International Congress on Advances in Non-impact Printing held in Washington, D.C. on Nov. 4 to 8, 1984, sponsored by the Society for Photographic Scientists and Engineers, there was described a development system using a donor roll and a magnetic roller. The donor roll and magnetic roller were electrically biased. The magnetic roller transported a two component developer material to the nip defined by the donor roll and magnetic roller, and toner is attracted to the donor roll from the magnetic roll. The donor roll is rotated synchronously with the photoconductive drum with the gap therebetween being about 0.20 millimeter. The large difference in potential between the donor roll and latent image recorded on the photoconductive drum causes the toner to jump across the gap from the donor roll to the latent image and thereby develop the latent image.
The following United States patents may be of interest:
U.S. Pat. No. 3,929,098 describes a developer sump located below a donor roll. A developer mix of toner particles and ferromagnetic carrier granules is in the sump. A cylinder having a magnet disposed therein rotates through the developer mix and conveys the developer mix adjacent the donor roll. An electrical field between the cylinder and donor roll loads the donor roll with toner particles.
U.S. Pat. No. 4,540,645 discloses a development apparatus using a magnetic roll contained within a nonmagnetic sleeve. A two component developer is supplied on the outer peripheral surface of the sleeve from a developer tank to form a magnetic brush. The developer material is brought into sliding contact with the photosensitive layer to develop the latent image with toner.
U.S. Pat. No. 4,565,437 describes a development system in which a photoconductive belt is wrapped around a portion of a first developer roller and spaced from a second developer roller. Each developer roller uses a magnet disposed interiorly of a nonmagnetic sleeve. The sleeves rotate to advance two component developer material into contact with the photoconductive belt thereby developing the latent image recorded thereon.
U.S. Pat. No. 4,809,034 discloses a developing device having a nonmagnetic developing sleeve. A magnetic roller is incorporated in the developing sleeve. A toner supply roller transports toner to the developing sleeve from the toner reservoir. The electrical potential on the supply roller is lower than that on the surface of the developing sleeve, thus the toner is attracted to the developing sleeve forming a brush of toner thereon. The developing sleeve conveys the brush of toner into contact with the photoconductive drum to develop the latent image recorded thereon.
U.S. Pat. No. 4,868,600 describes a scavengeless development system in which a donor roll has toner deposited thereon. A plurality of electrode wires are closely spaced to the donor roll in the gap between the donor roll and the photoconductive member. An AC voltage is applied to the electrode wires to detach toner from the donor roll and form a toner powder cloud in the gap. Toner from the toner powder cloud is attracted to the latent image recorded on the photoconductive member to develop the latent image recorded thereon. A conventional magnetic brush with conductive two component developer can be used for depositing the toner layer onto the donor roll. To prevent shorting between the conductive core of the donor roll and the AC biased wires or conductive magnetic brush, a resistive overcoating is selected. The conductive donor roll core is made from a material, such as metals or conductive particles, dispersed in a dielectric resin.
U.S. Pat. No. 4,338,222 discloses an electrically conducting composition comprising an organic hole transporting compound, and the reaction product of an organic hole transporting compound and an oxidizing agent capable of accepting one electron from the hole transporting compound.
In U.S. Pat. No. 5,300,339, the disclosure of which is totally incorporated herein by reference, there is illustrated a coated transport means comprised of a core with a coating comprised of charge transporting molecules and an oxidizing agent, or oxidizing agents dispersed in a binder.
It is an object of the present invention to provide improved coatings with many of the advantages illustrated herein.
Another object of the present invention is to provide improved donor roll coatings with many of the advantages illustrated herein.
Also, another object of the present invention is to provide improved toner donor roll coatings, which coatings enable improved conductivity uniformity and control in achieving a desired charge relaxation time constant with a molecular dispersion of a conductivity inducing component in the aforementioned overcoatings.
Another object of the present invention is to protect electrodes from wear.
Yet another object of the present invention is to prevent electrical shorting with conductive carrier beads.
Moreover, another object of the present invention relates to the provision of improved overcoatings for electrophotographic development subsystem donor rolls by the molecular dispersion of an oxidant in a charge transporting polymer,for example aryl diamine polymers, which enables, for example, improved and stable uniformity of the conductivity throughout the coating, and latitude and control in selecting a desired charge relaxation time constant of, for example, about 1 microsecond to about 10 seconds.
Also, another object of the present invention is to provide improved donor roll coatings, which coatings enable improved conductivity uniformity and control in achieving a desired charge relaxation time constant by varying the concentration of the charge transporting moiety in the backbone of the charge transporting aryl amine polymer.
Further, another object of the present invention is the provision of coatings comprised of doped polyether carbonate, PEC, obtained from the condensation of N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-hydroxy phenyl)-[1,1xe2x80x2-biphenyl]-4,4xe2x80x2-diamine and diethylene glycol bischloroformate, or variants thereof.
These and other objects of the present invention are accomplished in embodiments by the provision of certain coatings for various imaging systems.
In accordance with one aspect of the present invention, there is provided an apparatus for developing a latent image recorded on a surface. The apparatus includes a housing defining a chamber storing a supply of developer material comprising at least carrier and toner. A donor member with an improved coating thereover is comprised of, for example, a polymer which has an aryl diamine charge transporting moiety incorporated in the backbone, reference U.S. Pat. Nos. 4,618,551; 4,806,443; 4,806,444; 4,818,650; 4,935,487 and 4,956,440, the disclosures of which is totally incorporated herein by reference, and wherein an oxidant is molecularly dispersed in the aforementioned polyarylamine charge transport polymer, such as the polyether carbonate of the ""443 patent, and which roll is spaced from the surface and adapted to transport toner to a region opposed from the surface. In a hybrid scavengeless system, developer material containing toner, for example, of resin particles such as styrene acrylates, styrene methacrylates, styrene butadienes and pigment particles such as carbon black, contained in a housing is used to apply and maintain a toner layer on the donor roll. The developer roll and the donor member cooperate with one another to define a region wherein a substantially constant amount of toner having a substantially constant triboelectric charge is deposited on the donor member. The donor roll contains isolated electrodes within the surface which are overcoated with the improved coating, and the isolated electrodes are electrically biased to detach toner from the donor member so as to form a toner cloud in the space between the donor roll and latent image member. Detached toner from the toner cloud develops the latent image.
Pursuant to another embodiment of the present invention, there is provided an electrophotographic imaging or printing machine of the type in which an electrostatic latent image recorded on a photoconductive member is developed to form a visible image thereof, and wherein the improvement includes a housing defining a chamber storing a supply of developer material comprising at least carrier and toner. The coated donor member is spaced from the photoconductive member and adapted to transport toner to a region opposed from the photoconductive member. Developer material containing toner is used to apply and maintain a toner layer on the donor roll. The developer roll and the donor member cooperate with one another to define a region wherein a substantially constant amount of toner having a substantially constant triboelectric charge is deposited on the donor member. The donor roll contains isolated electrodes within the surface which are overcoated with the improved coating. The isolated electrodes are electrically biased to detach toner from the donor member so as to form a toner cloud in the space between the donor roll and latent image member. Detached toner from the toner cloud develops the latent image. The insulative donor roll core is made from dielectric materials such as vinyl ester, phenolic, polycarbonate, epoxy, and the like.
More specifically, in embodiments there are provided in accordance with the present invention certain overcoatings for toner transport rolls selected for the scavengeless and hybrid scavengeless systems mentioned herein. These overcoatings contain a partially oxidized charge transporting polymer and generally comprise least two constituents, a charge transporting polymer and an oxidizing agent. Various suitable charge transporting polymers, many of which are illustrated herein and described in the U.S. patents mentioned herein, may be utilized in the coatings of the present invention. These electrically active charge transporting polymeric materials should be capable of being oxidized by the oxidizing agent and be able to support the motion of holes through the unoxidized moiety in the charge transporting polymer. The charge transporting moiety in the backbone of the polymer can, for example, be an oxadiazole, hydrazone, carbazole, triphenylamine or diamine. Examples of charge transporting polymers include aryl amine compounds represented by the formula: 
wherein n is a repeating segment and can, for example, be a number between about 5 and about 5,000; Z is selected from the group consisting of: 
wherein n is 0 or 1; Ar represents an aromatic group selected from the group consisting of: 
wherein R is an alkylene radical selected from the group consisting of alkylene and iso-alkylene groups containing 2 to about 10 carbon atoms; Arxe2x80x2 is selected from the group consisting of: 
X is selected from the group consisting of: 
s is 0, 1 or 2; and Xxe2x80x2 is an alkylene radical selected from the group consisting of alkylene and iso-alkylene groups containing 2 to 10 carbon atoms.
Typical charge transporting polymers are represented by the following formula: 
wherein the value of n is between about 10 and about 1,000. These and other charge transporting polymers are described in U.S. Pat. No. 4,806,443, the disclosure thereof being totally incorporated herein by reference. One polymer selected as a coating and illustrated in the ""443 patent is a polyester carbonate which is a polymeric aryl amine obtained from the reaction of N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-hydroxyphenyl-(1,1xe2x80x2-biphenyl)-4,4xe2x80x2-diamine and diethylene glycol bischloroformate.
Other typical charge transporting polymers include aryl amine compounds represented by the formula: 
wherein R is selected from the group consisting of xe2x80x94H, alkyl like xe2x80x94CH3 and xe2x80x94C2H5; m is between about 4 and about 1,000; and A is selected from the group consisting of an aryl amine group represented by the formula: 
wherein m is 0 or 1; Z is selected from the group consisting of: 
wherein n is 0 or 1; Ar is selected from the group consisting of: 
wherein Rxe2x80x2 is selected from the group consisting of xe2x80x94CH3, xe2x80x94C2H5, xe2x80x94C3H7, and xe2x80x94C4H9; Arxe2x80x2 is selected from the group consisting of: 
X is selected from the group consisting of: 
B is selected from the group consisting of the aryl amine group as defined for A, and
xe2x80x94Ar"Parenopenst"V"Parenclosest"nArxe2x80x94
wherein Ar is as defined herein, and V is selected from the group consisting of: 
and n is 0 or 1. Specific examples include: 
where the value of m is between about 18 and about 19, and 
where the value of m is between about 4 and about 5. These and other charge transporting polymers represented by the above generic formula are described in U.S. Pat. Nos. 4,818,650 and 4,956,440, the disclosures thereof being totally incorporated herein by reference.
An example of other typical charge transporting polymers include: 
wherein the value of m was between about 10 and about 50. This and other similar charge transporting polymers are described in U.S. Pat. Nos. 4,806,444 and 4,956,487, the disclosures thereof being totally incorporated herein by reference.
Other examples of typical charge transporting polymers are: 
wherein m is between about 10 and about 10,000, and 
wherein m is between about 10 and about 1,000. Specific charge transporting polymers include copoly[3,3xe2x80x2bis(hydroxyethyl)triphenylamine/bisphenol A]carbonate, copoly[3,3xe2x80x2bis(hydroxyethyl)tetraphenylbenzidine/bisphenol A]carbonate, poly[3,3xe2x80x2bis(hydroxyethyl)tetraphenylbenzidine]carbonate, poly[3,3xe2x80x2bis(hydroxyethyl)triphenylamine]carbonate, and the like. These charge transporting polymers are described in U.S. Pat. No. 4,401,517, the disclosure thereof being totally incorporated herein by reference.
Further examples of charge transporting polymers include: 
where n is between about 5 and about 5,000; 
where n represents a number sufficient to achieve a weight average molecular weight of between about 20,000 and about 500,000; 
where n represents a number sufficient to achieve a weight average molecular weight of between about 20,000 and about 500,000; and 
where n represents a number sufficient to achieve a weight average molecular weight of between about 20,000 and about 500,000. These and other related charge transporting polymers are described in U.S. Pat. No. 5,030,532, the entire disclosure thereof being incorporated herein by reference. These coatings are comprised of an partially oxidized polyethercarbonate. More specifically, polyethercarbonate, which is a polymeric arylamine obtained from the reaction of, for example, N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-hydroxyphenyl)-(1,1xe2x80x2-biphenyl)-4,4xe2x80x2-diamine and bischloroformate, like diethylene glycol bischloroformate, reference U.S. Pat. No. 4,806,443, the disclosure of which is totally incorporated herein by reference, see especially Example 3 of this patent, is subjected to oxidation with an oxidizing agent like tris(4-bromophenyl)ammonium hexachloroanthimonate (TBTPAT). It is believed that in the presence of an oxidizing agent the partial oxidized charge transporting moieties like tetraphenyldiamines of the polymer function as carrier sites that are transported through the unoxidized charge transporting moieties
The oxidizing agent in the coating may be selected from a variety of materials. These include salts comprised of an anion selected from the group consisting of SbCl6xe2x88x92; SbCl4xe2x88x92 and PF6xe2x88x92 and a cation selected from the group consisting of a triphenyl methyl+; tetraethylammonium+; benzyl dimethylphenyl ammonium+; 2,4,6-trimethyl pyrillium+; Ag+; K+; Na+; NO+ such as tris(4-bromophenyl)ammonium hexachloroanthimonate (TBTPAT), ferric chloride, both hydrated and anhydrous, trifluoroacetic acid (TFA), and the like. Other oxidizing agents include 2,4,6-trinitrobenzene sulfonic acid; dichloromaleic anhydride; tetrabromophthalic anhydride; 2,7-dinitro-9-fluorenone; 2,4,7-trinitro-9-fluorenone; tetraphenyl phthalic anhydride; SeO2N2O4 and other similar oxidizing agents that accept one electron from the hole transporting polymer. More than one antioxidant can be employed.
One procedure for the preparation of the coating comprises adding the charge transporting polymer in a suitable solvent and stirring with a magnetic stirrer until a complete solution is achieved. The oxidant is added and the stirring continued to assure uniform distribution. The resulting films are coated from a solution of the charge transporting polymer and the oxidant in a solvent and is either bar, spray or dip coated. The solvents can be one or mixture of alkylene halides like methylene chloride, chlorobenzene, toluene, tetrahydrafuran or mixtures thereof. The concentration of the oxidant can range from 1 percent by weight up to about 50 percent by weight of the charge transporting polymer, and preferably from 2 weight percent to 15 weight percent and the exact concentration depends on the relaxation time requirements. The film thickness ranges from 5 microns to 50 micrometers depending on the application.